I've thought about this a long time and I come down on the side of not making faculty/staff on campuses empowered as agents of the state or school to act as pseudo-LEOs.
Being a teacher does not necessarily empower you to be captain of the ship or guardian of the class.
If one can obtain a permit/license to carry - it should be good on campuses.
Then you act accordingly to your values and the laws of self-defense - you have no added responsibility in a mandated fashion. If you want teachers to become LEOs - then they go to the academy and have the protections that officers have in post shooting incidents. They qualify every 4 months. They take intensive FOF training. They get liability protection and insurance coverage for their actions. That's if you want them to act pro-actively.
However, I do think it is morally mandated that if you talk the campus carry talk and get hissy about not having the priviledge you should train beyond the permit course (which is no tactical training). I've managed to get a fair amount of relevant training for a FOG - I'm no cop. But I have colleagues who rant about not being able to carry. So I say to them, if we went to the president and asked for permission to carry and he asked - well, what have you done to demonstrate competence? Many would have to say - Well, I shot a rock in the country and passed the trivial CHL test. And yes, I read Guns and Ammo. On the other hand, quite a few have significant training. Should the school have to parse this?
One hitch in a great deal of current debate is that the laws will only cover state schools and private schools will still be allowed to ban carry under the general provisions of the private property exemptions. That makes the latter schools more target attractive.
When I suggest this should not be the case, the private property zealots go nuts. They accept state mandates that they must have working toilets in their businesses or can't discriminate on race, etc. but then go crazy when one suggests they can't ban the right of self-defense. It's my castle, wah, wah!! So, don't have a business that invites folks in.
As far as the probability of you shooting an innocent: Schools are no different than other target rich, crowded places like malls or churches. You should be capable of knowing if you could take the shot.
Another psychological factor is that folks seem to have a principle that you don't take the life of an innocent even if it furthers the greater good. Meaning that for some reason it is better for more to die than kill an innocent to stop those deaths. Thus, the risk of a bystander taking a round, drives the argument for some.
I do appreciate the OP's analysis and don't think a reasoned approach is necessarily elitist. Unless the pros and cons are discussed without reflexive RKBAish rants - we get nowhere.
Note, I discussed faculty/staff carry - I am still mixed about student carry for several issues regarding the unusual nature of dorm life and the youngest possible carriers (21 years olds) that live on campus. They are in a different social circumstance than the returning mature adult student.
The current CCW/CHL folks tend to have a low trouble rate as they are older and seasoned by life. Students in dorms are a touch different and this issue takes more thought.
Last - most schools only care about liability issues and PR. Their programs are designed to be after the fact defenses against lawsuits and to maintain their images. They are focused on the best outcome for the corporate entity of the school and the outcome for the individuals (while sad and let's have a memorial service) is secondary.